High index fluorine-free phosphate glasses

ABSTRACT

This invention is drawn to fluorine-free glasses having refractive indices of at least 1.65 which generally consist, in mole percent, of: 
     
         ______________________________________                                    
 
    
     P 2  O 5         24-36                                              
ZnO                    0-45                                               
Li 2  O             0-15                                               
Na 2  O             0-20                                               
K 2  O              0-10                                               
Ag 2  O             0-25                                               
Tl 2  O             0-25                                               
Li 2  O + Na 2  O + K 2  O + Ag 2  O + Tl 2  O             
                       15-30                                              
PbO                    0-20                                               
CaO                    0-20                                               
CuO                    0-5                                                
CeO 2               0-2                                                
SrO                    0-20                                               
BaO                    0-20                                               
CaO + SrO + BaO        0-25                                               
Sb 2  O 3        0-61                                               
Bi 2  O 3        0-10                                               
Sb 2  O 3  + Bi 2  O 3                                        
                       0-61                                               
Sb 2  O 3  + Bi 2  O 3  + Ag 2  O + Tl 2  O             
                       7-76                                               
SnO                    0-5                                                
Al 2  O 3        0-5                                                
B 2  O 3         0-10                                               
Al 2  O 3  + B 2  O 3                                         
                       0-10                                               
______________________________________

BACKGROUND OF THE INVENTION

U.S. application Ser. No. 07/599,751, filed Oct. 19, 1990 by me underthe title FLUORINE-FREE PHOSPHATE GLASSES, now U.S. Pat. No. 5021,366,is directed to the preparation of chemically durable, weather resistant,essentially fluorine-free glass compositions with annealing pointswithin the range of about 300°-340° C., thereby enabling them to bemolded into lenses at temperatures of about 360°-400° C., and withrefractive indices of about 1.605 and linear coefficients of thermalexpansion (25°-300° C.) between 145-170×10⁻⁷ /°C. Those glasses weredesigned to replace the alkali metal fluoroaluminophosphate glassesdisclosed in U.S. Pat. No. 4,362,819 (Olszewski et al.) marketed byCorning Incorporated, Corning, New York for pressing optically finishedlenses as described in U.S. Pat. No. 4,481,023 (Marechal et al.) As wasexplained in that application, fluorine in the glasses attacked thesurfaces of the molds during pressing of the lenses, and volatilizationthereof during melting of the glass batch gave rise to environmentalhazards. The glasses of U.S. Ser. No. 07/599,751 consisted essentially,expressed in terms of mole percent on the oxide basis, of:

    ______________________________________                                        Li.sub.2 O   5-10    P.sub.2 O.sub.5 30-36                                    Na.sub.2 O   5-15    Al.sub.2 O.sub.3                                                                              0-5                                      K.sub.2 O    0-6     CeO.sub.2       0-2                                      Li.sub.2 O + Na.sub.2 O + K.sub.2 O                                                        15-25   SnO              0-20                                    ZnO          10-33   PbO              0-20                                    CaO          0-20    Sb.sub.2 O.sub.3                                                                               0-12                                    SrO          0-20    Bi.sub.2 O.sub.3                                                                              0-6                                      BaO          0-20    SnO + PbO + Sb.sub.2 O.sub.3 +                                                                 0-20                                                         Bi.sub.2 O.sub.3                                         ______________________________________                                    

The primary objective of the instant invention was to devisefluorine-free glass compositions demonstrating chemical and physicalproperties similar to those exhibited by the glasses of U.S. Ser. No.07/599,751, but wherein refractive indices ranging from at least 1.65 tovalues in excess of 1.8 can be achieved. In like manner to thedefinition set out in U.S. Ser. No. 07/599,751, the expressionessentially fluorine-free indicates that no material containingsubstantial concentrations of fluorine is intentionally included in theglass.

SUMMARY OF THE INVENTION

That objective can be attained in glasses having base compositionswithin the R₂ O-P₂ O₅ system, wherein R₂ O consists of at least onemetal oxide selected from the group consisting of Li₂ O, Na₂ O, K₂ O,Ag₂ O, and Tl₂ O. The compositions can desirably also contain at leastone metal oxide selected from the group consisting of Bi₂ O₃, PbO, andSb₂ O₃. At least one member of the group Ag₂ O, Bi₂ O₃, PbO, Sb₂ O₃, andTl₂ O must be present to assure attainment of the required highrefractive index, viz., at least 1.65, coupled with the desired lowannealing point, viz., 300°-340° C., and linear coefficient of thermalexpansion, viz., 135-180×10⁻⁷ /°C. over the temperature range 25°-300°C. Hence, more specifically, the inventive glasses consist essentially,expressed in terms of mole percent on the oxide basis, of:

    ______________________________________                                        P.sub.2 O.sub.5 24-36   SrO           0-20                                    ZnO             0-45    BaO           0-20                                    Li.sub.2 O      0-15    CaO + SrO + BaO                                                                             0-25                                    Na.sub.2 O      0-20    Sb.sub.2 O.sub.3                                                                            0-61                                    K.sub.2 O       0-10    Bi.sub.2 O.sub.3                                                                            0-10                                    Ag.sub.2 O      0-25    Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         0-61                                    Tl.sub.2 O      0-25    Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         7-76                                                            Ag.sub.2 O + Tl.sub.2 O                               Li.sub.2 O + Na.sub.2 O + K.sub.2 O +                                                         15-30   SnO           0-5                                     Ag.sub.2 O + Tl.sub.2 O                                                       PbO             0-20    Al.sub.2 O.sub.3                                                                            0-5                                     CuO             0-5     B.sub.2 O.sub.3                                                                             0-10                                    CaO             0-20    Al.sub.2 O.sub.3 + B.sub.2 O.sub.3                                                          0-10                                    CeO.sub.2       0-2                                                           ______________________________________                                    

with the provisos that:

(a) in the absence of Sb₂ O₃ and/or Bi₂ O₃, the total Ag₂ O+Tl₂ O willrange 11-25;

(b) in the absence of Ag₂ O and/or Tl₂ O, the total Sb₂ O₃ +Bi₂ O₃ willrange 7-61;

(c) when present in the absence of Bi₂ O₃ and/or Ag₂ O and/or Tl₂ O, Sb₂O₃ will range 10-61 and, when present in the absence of Sb₂ O₃ and/orAg₂ O and/or Tl₂ O, Bi₂ O₃ will range 7-10;

(d) when present in the absence of Bi₂ O₃, Sb₂ O₃, and Tl ₂ O, Ag₂ Owill range 13-25; and

(e) when present in the absence of Ag₂ O, Bi₂ O₃, and Sb₂ O₃, Tl₂ O willrange 11-25.

As will be appreciated, the required combination of chemical andphysical properties demands that the above-outlined compositionintervals be strictly observed, with special attention being directed tothe levels of Ag₂ O, Bi₂ O₃, Sb₂ O₃, and Tl₂ O. Thus, their inclusionraises the refractive index of the base glass as desired, but alsoimpacts upon other properties of the glass for which compensation mustbe made. To illustrate:

Ag₂ O and Tl₂ O behave in like manner to the alkali metal oxides insoftening the glass, i.e., lowering the annealing point thereof. At thesame time, however, they adversely affect the chemical durability andweatherability of the glasses.

The inclusion of alkaline earth metal oxides acts to raise therefractive index of the glass somewhat without increasing the dispersiontherein and raising the annealing point thereof, while also improvingthe chemical durability thereof. Nevertheless, when the totalconcentration of alkaline earth metal oxides exceeds 25%, the glassesbecome quite susceptible to devitrification.

Whereas the addition of PbO to a glass composition is well-recognized inthe art as raising the refractive index thereof, its inclusion increasesthe dispersion therein. Moreover, the linear coefficient of thermalexpansion is raised significantly through the addition of PbO to theinventive base compositions which must be offset through the addition ofSb₂ O₃ and/or SnO and/or Al ₂ O₃ and/or B₂ O₃ and/or alkaline earthmetal oxides. Consequently, whereas PbO can be tolerated in theinventive glasses, it will desirably be maintained at a relatively lowlevel.

As was alluded to immediately above, Al₂ O₃, B₂ O₃, and SnO act toenhance the chemical durability of the inventive glasses. Theconcentrations thereof must be held at low concentrations, however, toavoid elevating the annealing point of the glass outside of the desiredrange.

Sb₂ O₃ is more preferred than Bi₂ O₃ for raising the refractive-index.It is less subject to reducing conditions and is much more soluble inthe base glass than Bi₂ O₃. Ag₂ O and Tl₂ O exert an extreme effect uponthe refractive index of the glass. That is, the refractive indexcommonly increases by about 0.008 per mole percent addition of Tl₂ O andby about 0.0065 per mole percent addition of Ag₂ O. Tl ₂ O demonstratesa further advantage over Ag₂ O in that the glasses are characterized bybetter weatherability.

When desired, CeO₂ may be included to render the glasses resistant tosuch radiations as x-radiations.

Whereas it is not mathematically possible to convert compositionintervals expressed in terms of mole percent to exact composition rangesdescribed in terms of weight percent, the following values representapproximations of the compositions of the inventive glasses defined interms of weight percent:

    ______________________________________                                        P.sub.2 O.sub.5                                                                          11.1-47.2 SrO           0-11.1                                     ZnO        0-34.2    BaO           0-25.9                                     Li.sub.2 O 0-4.5     CaO + SrO + BaO                                                                             0-29.7                                     Na.sub.2 O 0-12.2    Sb.sub.2 O.sub.3                                                                            0-82.0                                     K.sub.2 O  0-9.2     Bi.sub.2 O.sub.3                                                                            0-39.6                                     Ag.sub.2 O 0-46.5    Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         0-83.4                                     Tl.sub.2 O 0-61.4    Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         17.5-88.8                                                       Ag.sub.2 O + Tl.sub.2 O                                  Li.sub.2 O + Na.sub.2 O +                                                                1.9-64.4  SnO           0-7.3                                      K.sub.2 O + Ag.sub.2 O +                                                      Tl.sub.2 O                                                                    PbO        0-34.3    Al.sub.2 O.sub.3                                                                            0-5.1                                      CaO        0-12.2    B.sub.2 O.sub.3                                                                             0-7.0                                      CuO        0-4.0     Al.sub.2 O.sub.3 + B.sub.2 O.sub.3                                                          0-8.4                                      CeO.sub.2  0-4.0                                                              ______________________________________                                    

with the provisos that:

(a) in the absence of Sb₂ O₃ and/or Bi₂ O₃, the total Ag₂ O+Tl₂ O willrange 17.7-64.4;

(b) in the absence of Ag₂ O and/or Tl₂ O, the total Sb₂ O_(3+Bi) ₂ O₃will range 17.5-83.4;

(c) when present in the absence of Bi₂ O₃ and/or Ag₂ O and/or Tl₂ O, Sb₂O₃ will range 17.5-82.0 and, when present in the absence of Sb₂ O₃and/or Ag₂ O and/or Tl₂ O, Bi₂ O₃ will range 18.7-39.6;

(d) when present in the absence of Bi₂ O₃, Sb₂ O₃, and Tl₂ O, Ag₂ O willrange 17.7-46.5; and

(e) when present in the absence of Ag₂ O, Bi₂ O₃, and Sb₂ O₃, Tl₂ willrange 24.8-61.4.

In essence, the instant inventive glasses are founded in the utilizationof at least one of the group Ag₂ O, Bi₂ O₃, Sb₂ O₃, and Tl₂ O to raisethe refractive index of the glasses disclosed in U.S. Ser. No.07/599,751, but wherein the concentrations of the other components ofthe latter glasses have been altered to produce products exhibiting thedesired ranges of chemical and physical properties.

PRIOR ART

In addition to U.S. Ser. No. 07/599,751, the following patent is alsobelieved to have relevance to the instant inventive glasses:

U.S. Pat. No. 3,853,568 (Chvatal) discloses three groups of Ag₂O-containing glass compositions, one of which comprised, in weightpercent, 20-70% Ag₂ O and 30-80% of two oxides selected from the groupof As₂ O₃, B₂ O₃, Bi₂ O₃, GeO₂, P₂ O₅, Sb₂ O₃, and TeO₂. The patentreferred to the following two ranges of components within that groupwhich are pertinent to the present inventive glasses:

    ______________________________________                                        Sb.sub.2 O.sub.3                                                                      10-45     Ag.sub.2 O                                                                            20-60   P.sub.2 O.sub.5                                                                    30-50                                  Bi.sub.2 O.sub.3                                                                      10-45     Ag.sub.2 O                                                                            20-60   P.sub.2 O.sub.5                                                                    30-45                                  ______________________________________                                    

Whereas partial overlap may be possible between those ranges and thoseof the inventive glasses, no mention is made in the patent to pressinglenses and the chemical and physical properties required in glassesdestined for that application, and none of the working examples suppliedin the patent had a composition coming within the ranges of theinventive glasses.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Table I records a group of glass compositions melted on a laboratoryscale and reported in terms of mole percent on the oxide basisillustrating the parameters of the present inventive glasses. Table IAlists the same group of compositions expressed in terms of parts byweight on the oxide basis. Inasmuch as the sum of the individualcomponents recited in Table IA totals or very closely approximates 100,for all practical purposes the tabulated values may be deemed to reflectweight percent. The actual batch ingredients can comprise any materials,either oxides or other compounds, which, when melted in combination withthe other constituents, will be converted into the desired oxide in theproper proportions. For example, zinc orthophosphate may be employed asa source of ZnO and P₂ O₅, and Li₂ CO₃ and AgNO₃ may comprise thesources of Li₂ O and Ag₂ O, respectively.

The batch ingredients were compounded, tumble mixed together to aid inobtaining a homogeneous melt, and then charged into platinum crucibles.After placing lids thereon, the crucibles were moved into a furnaceoperating at about 900°-1200° C. and the batches melted for about threehours. Thereafter, the melts were poured into steel molds to produceglass slabs having dimensions of about 6"×4"×0.5" which were transferredimmediately to an annealer operating at about 300°-325° C.

(Whereas the above description reflects melting on a laboratory scaleonly, it must be appreciated that large scale melts thereof can beconducted in commercial melting units. Thus, it is only necessary thatthe batch materials be melted at a temperature and for a time sufficientto secure a homogeneous melt.)

                  TABLE I                                                         ______________________________________                                        (Mole Percent)                                                                ______________________________________                                               1      2      3     4    5    6     7    8                             ______________________________________                                        Li.sub.2 O                                                                           7.0    7.0    7.0   7.0  7.0  7.0   7.0  6.6                           Na.sub.2 O                                                                           8.0    8.0    8.0   8.0  8.0  8.0   8.0  7.5                           K.sub.2 O                                                                            5.0    5.0    5.0   5.0  --   --    --   --                            ZnO    13.5   11.0   10.0  21.0 18.5 13.5  11.0 9.4                           CaO    10.0   10.0   10.0  7.5  10.0 10.0  10.0 9.4                           BaO    5.0    5.0    3.5   7.5  5.0  5.0   5.0  3.3                           SnO    1.0    1.0    1.0   1.0  1.0  1.0   1.0  0.9                           Sb.sub.2 O.sub.3                                                                     15.0   17.5   20.0  --   10.0 15.0  17.5 18.7                          Bi.sub.2 O.sub.3                                                                     --     --     --    8.0  --   --    --   --                            Tl.sub.2 O                                                                           --     --     --    --   5.0  5.0   5.0  11.0                          Al.sub.2 O.sub.3                                                                     0.5    0.5    0.5   --   0.5  0.5   0.5  0.5                           P.sub.2 O.sub.5                                                                      35.0   35.0   35.0  35.0 35.0 35.0  35.0 32.7                          ______________________________________                                               9      10     11    12   13   14    15   16                            ______________________________________                                        Li.sub.2 O                                                                           7.0    7.0    7.0   7.0  7.0  7.0   7.0  6.1                           Na.sub.2 O                                                                           8.0    8.0    8.0   8.0  8.0  8.0   8.0  7.0                           K.sub.2 O                                                                            5.0    5.0    5.0   5.0  5.0  5.0   5.0  4.4                           ZnO    10.0   10.0   10.0  18.5 8.5  --    --   2.5                           CaO    6.8    1.8    3.5   --   --   --    --   --                            BaO    6.7    1.7    --    --   --   --    --   --                            SnO    1.0    1.0    1.0   1.0  1.0  1.0   1.0  1.0                           PbO    --     --     --    --   --   --    --   20.0                          Sb.sub.2 O.sub.3                                                                     20.0   30.0   30.0  25.0 35.0 43.5  46.0 21.8                          Al.sub.2 O.sub.3                                                                     0.5    0.5    0.5   0.5  0.5  0.5   0.5  2.2                           P.sub.2 O.sub.5                                                                      35.0   35.0   35.0  35.0 35.0 35.0  32.5 35.0                          ______________________________________                                               17     18     19    20   21   22    23   24                            ______________________________________                                        Li.sub.2 O                                                                           7.0    --     --    --   --   --    --   --                            Na.sub.2 O                                                                           8.0    --     --    --   --   --    --   --                            K.sub.2 O                                                                            5.0    --     --    --   --   --    --   --                            ZnO    2.5    45.0   30.0  15.0 44.0 29.0  15.0 13.5                          SnO    1.0    --     --    --   1.0  1.0   --   1.0                           PbO    17.5   --     --    --   --   --    --   --                            Sb.sub.2 O.sub.3                                                                     23.0   --     15.0  30.0 --   15.0  30.0 30.0                          Al.sub.2 O.sub.3                                                                     2.2    2.0    --    --   2.0  2.0   --   0.5                           Ag.sub.2 O                                                                           --     20.0   20.0  20.0 --   --    --   --                            Tl.sub.2 O                                                                           --     --     --    --   20.0 20.0  20.0 20.0                          P.sub.2 O.sub.5                                                                      33.8   33.0   35.0  35.0 33.0 33.0  35.0 35.0                          ______________________________________                                               25     26     27    28   29   30    31   32                            ______________________________________                                        Li.sub.2 O                                                                           --     7.0    6.7   7.0  5.3  7.0   7.0  7.0                           Na.sub.2 O                                                                           --     8.0    7.6   8.0  6.0  8.0   8.0  8.0                           K.sub.2 O                                                                            --     5.0    4.8   5.0  3.7  5.0   --   --                            ZnO    --     --     9.5   --   --   23.5  24.5 24.5                          CaO    --     7.5    9.5   --   --   10.0  11.3 11.3                          BaO    --     7.5    3.3   --   --   5.0   3.7  3.7                           SnO    1.0    1.0    1.0   --   --   --    1.0  --                            Sb.sub.2 O.sub.3                                                                     43.5   28.5   19.1  55.0 53.0 --    4.1  4.1                           Bi.sub.2 O.sub.3                                                                     --     --     --    --   --   6.0   --   --                            Al.sub.2 O.sub.3                                                                     --     0.5    0.5   --   --   0.5   0.4  0.4                           Ag.sub.2 O                                                                           --     --     --    --   --   --    --   5.0                           Tl.sub.2 O                                                                           20.0   --     --    --   --   --    5.0  --                            P.sub.2 O.sub.5                                                                      35.0   35.0   33.3  25.0 30.0 35.0  35.0 35.0                          CuO    --     --     --    --   2.0  --    --   --                            B.sub.2 O.sub.3                                                                      --     --     5.0   --   --   --    --   --                            ______________________________________                                    

                  TABLE IA                                                        ______________________________________                                        (Parts By Weight)                                                             ______________________________________                                               1      2      3     4    5    6     7    8                             ______________________________________                                        Li.sub.2 O                                                                           1.6    1.5    1.5   1.6  1.5  1.4   1.4  1.1                           Na.sub.2 O                                                                           3.8    3.6    3.5   3.7  3.6  8.0   8.0  2.7                           K.sub.2 O                                                                            3.6    3.4    3.3   3.5  --   --    --   --                            ZnO    8.4    6.5    5.8   12.8 10.9 7.4   5.8  4.4                           CaO    4.3    4.1    4.0   3.2  4.1  3.8   3.7  3.0                           BaO    5.8    5.6    3.8   8.6  5.6  5.2   5.0  2.9                           SnO    1.2    1.1    1.1   1.1  1.1  1.0   1.0  0.8                           Sb.sub.2 O.sub.3                                                                     33.2   37.3   41.3  --   21.2 29.5  33.3 31.3                          Bi.sub.2 O.sub.3                                                                     --     --     --    28.0 --   --    --   --                            Tl.sub.2 O                                                                           --     --     --    --   15.4 14.3  13.8 26.8                          Al.sub.2 O.sub.3                                                                     0.4    0.4    0.4   --   0.4  0.3   0.3  0.3                           P.sub.2 O.sub.5                                                                      41.0   36.3   35.2  37.3 36.1 33.5  32.4 26.6                          ______________________________________                                               9      10     11    12   13   14    15   16                            ______________________________________                                        Li.sub.2 O                                                                           1.5    1.3    1.3   1.4  1.2  1.1   1.1  1.1                           Na.sub.2 O                                                                           3.4    3.0    3.1   3.3  2.9  2.6   2.6  2.5                           K.sub.2 O                                                                            3.3    2.9    2.9   3.1  2.7  2.5   2.4  2.4                           ZnO    5.6    5.0    5.0   9.9  4.0  --    --   1.2                           CaO    2.6    0.6    1.2   --   --   --    --   --                            BaO    7.2    1.7    --    --   --   --    --   --                            SnO    1.0    0.9    0.9   1.0  0.9  0.8   0.8  0.9                           Sb.sub.2 O.sub.3                                                                     40.4   53.7   54.2  48.1 59.1 66.5  69.0 36.5                          Al.sub.2 O.sub.3                                                                     0.4    0.3    0.3   0.3  0.3  0.3   0.3  1.3                           P.sub.2 O.sub.5                                                                      34.4   30.5   30.8  32.8 28.8 26.1  23.7 28.5                          ______________________________________                                               17     18     19    20   21   22    23   24                            ______________________________________                                        Li.sub.2 O                                                                           1.2    --     --    --   --   --    --   --                            Na.sub.2 O                                                                           2.9    --     --    --   --   --    --   --                            K.sub.2 O                                                                            2.7    --     --    --   --   --    --   --                            ZnO    1.2    27.8   14.9  6.2  20.9 11.6  5.2  4.7                           Ag.sub.2 O                                                                           --     35.2   28.2  23.7 --   --    --   --                            PbO    22.7   --     --    --   --   --    --   --                            SnO    0.8    --     --    --   0.9  0.7   --   0.6                           Sb.sub.2 O.sub.3                                                                     39.0   --     26.6  44.6 --   27.6  37.3 37.2                          Tl.sub.2 O                                                                           --     --     --    --   49.6 41.9  36.2 36.1                          Al.sub.2 O.sub.3                                                                     1.3    1.6    --    --   1.2  1.0   --   0.2                           P.sub.2 O.sub.5                                                                      27.9   33.5   30.2  25.4 27.4 23.1  21.2 21.1                          ______________________________________                                               25     26     27    28   29   30    31   32                            ______________________________________                                        Li.sub.2 O                                                                           --     1.3    1.5   1.0  0.8  1.7   1.7  1.8                           Na.sub.2 O                                                                           --     3.1    3.4   2.4  1.8  4.1   4.0  4.4                           K.sub.2 O                                                                            --     2.9    3.3   2.3  1.7  3.9   --   --                            ZnO    --     --     5.6   --   --   15.6  16.1 18.3                          CaO    --     2.6    3.9   --   --   4.6   5.1  5.6                           BaO    --     7.1    3.7   --   --   6.3   4.6  5.1                           SnO    0.6    0.9    1.0   --   --   --    1.2  --                            Sb.sub.2 O.sub.3                                                                     48.1   51.1   40.3  77.0 74.3 --    9.7  10.5                          Bi.sub.2 O.sub.3                                                                     --     --     --    --   --   22.9  --   --                            Tl.sub.2 O                                                                           32.2   --     --    --   --   --    17.1 --                            Al.sub.2 O.sub.3                                                                     0.2    0.3    0.4   --   --   0.4   0.3  0.4                           P.sub.2 O.sub.5                                                                      18.8   30.6   34.4  17.1 20.5 40.6  40.1 43.8                          CuO    --     --     --    --   0.8  --    --   --                            B.sub.2 O.sub.3                                                                      --     --     2.4   --   --   --    --   --                            Ag.sub.2 O                                                                           --     --     --    --   --   --    --   10.2                          ______________________________________                                    

Table II records the softening point (S.P.) and the annealing point(A.P.) in °C., the linear coefficient of thermal expansion (Exp) overthe temperature interval 25°-300° C. expressed in terms of ×10⁷⁻ /°C,the refractive index (n_(D)), and the dispersion (ν) determined inaccordance with measuring techniques conventional in the glass art.Table II also reports the weight loss (W.L.) expressed in terms ofpercent demonstrated by the glasses after an immersion for six hours ina bath of boiling deionized water, and a qualitative analysis of theweatherability (Weath) of the glasses based upon the visual appearancethereof after an exposure in a humidity cabinet for 500 hours at 60° C.and 98% relative humidity. A weight loss greater than 0.33% isconsidered to represent unsatisfactory chemical durability, with lossesless than 0.1% being greatly preferred. Legends for the weatherabilitycharacter exhibited include: nc =no change in appearance; xl =extremelylight frosted appearances; vl =very light frosted appearance; lt =lightfrosted appearance; and hf =heavy frosted appearance. The most preferredglasses will display no frosting or haze. Where haze can be observedonly when the glass is viewed at a small angle (exemplified by xl andvl), however, the glasses will be satisfactory for use in mostapplications. (When subjected to the above-described weatherabilitytest, the current commercial glass produced under U.S. Pat. No.4,362,819, supra, exhibits a very light frosted appearance.)

                                      TABLE II                                    __________________________________________________________________________         1   2   3   4   5   6   7   8                                            __________________________________________________________________________    S.P. 438 445 437 .sup.˜ 440                                                                  426 --  --  --                                           A.P. 333 336 333 .sup.˜ 335                                                                  .sup.˜ 325                                                                  --  --  --                                           Exp. 153 149 152 .sup.˜ 153                                                                  --  --  --  --                                           n.sub.D                                                                             1.682                                                                             1.696                                                                             1.710                                                                            .sup.˜ 1.670                                                                 1.686                                                                            1.72                                                                              .sup.˜ 1.73                                                                 1.77                                         ν  40  35 --   .sup.˜ 40                                                                  --  --  --  --                                           W.L. 0.02                                                                              0.02                                                                              0.04                                                                              0.01                                                                              0.01                                                                              0.00                                                                              --  --                                           Weath                                                                              nc  nc  nc  --  nc  nc  nc  nc                                           __________________________________________________________________________         9   10  11  12  13  14  15  16                                           __________________________________________________________________________    S.P. 433 414 415 409 407 396 396 .sup.˜ 410                             A.P. .sup.˜ 330                                                                  .sup.˜ 315                                                                  .sup.˜ 315                                                                  .sup.˜ 310                                                                  .sup.˜ 310                                                                  .sup.˜ 300                                                                  .sup.˜ 300                                                                  .sup.˜ 310                             Exp. --  169 162 160 160 164 180 --                                           n.sub.D                                                                            1.71                                                                              1.75                                                                               1.755                                                                            1.72                                                                              1.77                                                                              1.83                                                                              >1.80                                                                             .sup.˜ 1.77                            W.L. 0.04                                                                              0.26                                                                              0.22                                                                              0.19                                                                              0.21                                                                              0.24                                                                              0.27                                                                              0.01                                         Weath                                                                              nc  nc  nc  vl  nc  nc  nc  xl                                           __________________________________________________________________________         17  18  19  20  21  22  23  24                                           __________________________________________________________________________    S.P. .sup.˜ 400                                                                  372 --  --  416 419 --  --                                           A.P. .sup.˜ 300                                                                  .sup.˜ 280                                                                  --  --  .sup.˜ 315                                                                  .sup.˜ 320                                                                   0   0                                           n.sub.D                                                                            1.76                                                                               1.681                                                                             1.760                                                                            >1.80                                                                              1.696                                                                             1.783                                                                            >1.80                                                                             >1.80                                        W.L. 0.01                                                                              0.04                                                                              0.05                                                                              --  0.02                                                                              0.01                                                                              --  --                                           Weath                                                                              xl  --  --  --  --  --  nc  nc                                           __________________________________________________________________________         25  26  27  28  29  30  31  32                                           __________________________________________________________________________    S.P. --  .sup.˜ 445                                                                  .sup.˜ 450                                                                  .sup.˜ 382                                                                  .sup.˜ 400                                                                  435 420 .sup.˜ 405                             A.P. --  336 .sup.˜ 345                                                                  --  --  325 .sup.˜ 320                                                                  307                                          Exp. --  160 139 --  --  149 --  150                                          n.sub.D                                                                            >1.80                                                                             .sup.˜ 1.79                                                                 .sup.˜ 1.71                                                                 1.86                                                                              >1.8                                                                               1.644                                                                             1.643                                                                             1.638                                       ν --  --  --  --  --   43 --  --                                           W.L. --  --  0.02                                                                              --  --  0.00                                                                              --  0.01                                         Weath                                                                              nc  nc  nc  vl  --  hf  nc  lt                                           __________________________________________________________________________

As can be observed from the above Tables, Examples 30-32 illustrateglasses having compositions somewhat outside of the ranges yieldingglasses demonstrating the desired chemical and physical properties. Thatis, because of the lack of control of the amounts and theinterrelationships existing between the individual components, one ormore of the properties listed in Table II will not be satisfactory.

Based upon an overall appraisal of the chemical and physical propertiesdemonstrated by the inventive glasses in conjunction with their meltingand forming characteristics, the preferred glasses consist essentially,expressed in terms of mole percent on the oxide basis, of

    ______________________________________                                        P.sub.2 O.sub.5                                                                             25-35    SrO           0-20                                     ZnO            0-35    BaO           0-20                                     Li.sub.2 O     0-10    CaO + SrO + BaO                                                                             0-20                                     Na.sub.2 O     0-15    Sb.sub.2 O.sub.3                                                                            0-61                                     K.sub.2 O     0-6      Bi.sub.2 O.sub.3                                                                            0-10                                     Ag.sub.2 O     0-25    Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         0-61                                     Tl.sub.2 O     0-25    Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         7-76                                                            Ag.sub.2 O + Tl.sub.2 O                                Li.sub.2 ONa.sub.2 O + K.sub.2 O +                                                          15-25    SnO           0-2                                      Ag.sub.2 O + Tl.sub.2 O                                                       PbO            0-20    Al.sub.2 O.sub.3                                                                            0-3                                      CuO           0-3      B.sub.2 O.sub.3                                                                             0-3                                      CaO            0-20    Al.sub.2 O.sub.3 + B.sub.2 O.sub.3                                                          0-5                                      CeO.sub.2     0-2                                                             ______________________________________                                    

The most preferred composition for a glass having a refractive index˜1.7 is Example 3 and for a glass having a refractive index ˜1. 8 isExample 14.

Although the inventive glasses were designed particularly for beingpress molded into optically finished lenses, their chemical and physicalproperties recommend their utility in preparing glass-plastic alloys ofthe type described in U.S. application Ser. No. 07/403,655, filed Sep.11, 1989, under the title GLASS/GLASS-CERAMIC-PLASTIC ALLOY ARTICLES byW. A. Bahn et al. now U.S. Pat. No. 5043,369.

I claim
 1. A glass having a composition which is essentiallyfluorine-free and which exhibits an annealing point between 300°-340°C., a linear coefficient of thermal expansion over the temperatureinterval 25°-300° C. between 135-180×10 ⁻⁷ /°C., a refractive index ofat least 1.65, and a weight loss after exposure to boiling water for sixhours no greater than 0.33% consisting essentially, expressed in termsof mole percent on the oxide basis, of:

    ______________________________________                                        P.sub.2 O.sub.5        24-36                                                  ZnO                    0-45                                                   Li.sub.2 O             0-15                                                   Na.sub.2 O             0-20                                                   K.sub.2 O              0-10                                                   Ag.sub.2 O             0-25                                                   Tl.sub.2 O             0-25                                                   Li.sub.2 O + Na.sub.2 O + K.sub.2 O + Ag.sub.2 O + Tl.sub.2 O                                        15-30                                                  PbO                    0-20                                                   CaO                    0-20                                                   CuO                    0-5                                                    CeO.sub.2              0-2                                                    SrO                    0-20                                                   BaO                    0-20                                                   CaO + SrO + BaO        0-25                                                   Sb.sub.2 O.sub.3       0-61                                                   Bi.sub.2 O.sub.3       0-10                                                   Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                                  0-61                                                   Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3 + Ag.sub.2 O + Tl.sub.2 O                                        7-76                                                   SnO                    0-5                                                    Al.sub.2 O.sub.3       0-5                                                    B.sub.2 O.sub.3        0-10                                                   Al.sub.2 O.sub.3 + B.sub.2 O.sub.3                                                                   0-10                                                   ______________________________________                                    

with the provisos that: (a) in the absence of Sb₂ O₃ and/or Bi₂ O₃, thetotal Ag₂ O+Tl₂ O will range 11-25; (b) in the absence of Ag20 and/orTl₂ O, the total Sb₂ O₃ +Bi₂ O₃ will range 7-61; (c) when present in theabsence of Bi₂ O and/or Ag₂ O and/or Tl₂ O, Sb₃ O₃ will range 10-61 and,when present in the absence of Sb₂ O₃ and/or Ag₂ O and/or Tl₂ O, Bi₂ O₃will range 7-10; (d) when present in the absence of Bi₂ O₃, Sb₂ O₃, andTl₂ O, Ag₂ O will range 13-25; and (e) when present in the absence ofAg₂ O, Bi₂ O₃, and Sb₂ O₃, Tl₂ O will range 11-25.
 2. A glass accordingto claim 1 consisting essentially of:

    ______________________________________                                        P.sub.2 O.sub.5                                                                             25-35    SrO           0-20                                     ZnO           0-35     BaO           0-20                                     Li.sub.2 O    0-10     CaO + SrO + BaO                                                                             0-20                                     Na.sub.2 O    0-15     Sb.sub.2 O.sub.3                                                                            0-61                                     K.sub.2 O     0-6      Bi.sub.2 O.sub.3                                                                            0-10                                     Ag.sub.2 O    0-25     Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         0-61                                     Tl.sub.2 O    0-25     Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         7-76                                                            Ag.sub.2 O + Tl.sub.2 O                                Li.sub.2 O + Na.sub.2 O + K.sub.2 O +                                                       15-25    SnO           0-2                                      Ag.sub.2 O + Tl.sub.2 O                                                       PbO           0-20     Al.sub.2 O.sub.3                                                                            0-3                                      CuO           0-3      B.sub.2 O.sub.3                                                                             0-3                                      CaO           0-20     Al.sub.2 O.sub.3 + B.sub.2 O.sub.3                                                          0-5                                      CeO.sub.2     0-2.                                                            ______________________________________                                    


3. A lens prepared from a glass having a composition which isessentially fluorine-free and which exhibits an annealing point between300°-340° C., a linear coefficient of thermal expansion over thetemperature interval 25°-300° C. between 135-180×10⁻⁷ /°C., a refractiveindex of at least 1.65, and a weight loss after exposure to boilingwater for six hours no greater than 0.33% consisting essentially,expressed in terms of mole percent on the oxide basis, of:

    ______________________________________                                        P.sub.2 O.sub.5        24-36                                                  ZnO                    0-45                                                   Li.sub.2 O             0-15                                                   Na.sub.2 O             0-20                                                   K.sub.2 O              0-10                                                   Ag.sub.2 O             0-25                                                   Tl.sub.2 O             0-25                                                   Li.sub.2 O + Na.sub.2 O + K.sub.2 O + Ag.sub.2 O + Tl.sub.2 O                                        15-30                                                  PbO                    0-20                                                   CaO                    0-20                                                   CuO                    0-5                                                    CeO.sub.2              0-2                                                    SrO                    0-20                                                   BaO                    0-20                                                   CaO + SrO + BaO        0-25                                                   Sb.sub.2 O.sub.3       0-61                                                   Bi.sub.2 O.sub.3       0-10                                                   Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                                  0-61                                                   Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3 + Ag.sub.2 O + Tl.sub.2 O                                        7-76                                                   SnO                    0-5                                                    Al.sub.2 O.sub.3       0-5                                                    B.sub.2 O.sub.3        0-10                                                   Al.sub.2 O.sub.3 + B.sub.2 O.sub.3                                                                   0-10                                                   ______________________________________                                    

with the provisos that: (a) in the absence of Sb₂ O₃ and/or Bi₂ O₃, thetotal Ag₂ O+Tl₂ O will range 11-25; (b) in the absence of Ag₂ O and/orTl₂ O, the total Sb₂ O₃ +Bi₂ O₃ will range 714 61; (c) when present inthe absence of Bi₂ O₃ and/or Ag₂ O and/or Tl₂ O, Sb₂ O₃ will range 10-61and, when present in the absence of Sb₂ O₃ and/or Ag₂ O and/or Tl₂ O₃will range 7-10; (d) when present in the absence of Bi₂ O₃, Sb₂ O₃, andTl₂ O, Ag₂ O will range 13-25; and (e) when present in the absence ofAg₂ O, Bi₂ O₃, and Sb₂ O₃, Tl₂ O will range 11-25.
 4. A lens accordingto claim 3 prepared from a glass having a composition consistingessentially of:

    ______________________________________                                        P.sub.2 O.sub.5                                                                             25-35    SrO           0-20                                     ZnO           0-35     BaO           0-20                                     Li.sub.2 O    0-10     CaO + SrO + BaO                                                                             0-20                                     Na.sub.2 O    0-15     Sb.sub.2 O.sub.3                                                                            0-61                                     K.sub.2 O     0-6      Bi.sub.2 O.sub.3                                                                            0-10                                     Ag.sub.2 O    0-25     Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         0-61                                     Tl.sub.2 O    0-25     Sb.sub.2 O.sub.3 + Bi.sub.2 O.sub.3                                                         7-76                                                            Ag.sub.2 O + Tl.sub.2 O                                Li.sub.2 O + Na.sub.2 O + K.sub.2 O +                                                       15-25    SnO           0-2                                      Ag.sub.2 O + Tl.sub.2 O                                                       PbO           0-20     Al.sub.2 O.sub.3                                                                            0-3                                      CuO           0-3      B.sub.2 O.sub.3                                                                             0-3                                      CaO           0-20     Al.sub.2 O.sub.3 + B.sub.2 O.sub.3                                                          0-5                                      CeO.sub.2     0-2.                                                            ______________________________________                                    